This invention relates generally to the field of material or article loading and unloading, and specifically, to the unloading of Bulk Mail Containers (BMCs).
Devices for unloading containers exist in many forms. Few of these, however, are suitable for free standing use in an enclosed environment. Unloaders for U.S. Post Office Bulk Mail Containers are even less common. Those that do exist, for example, the Lockheed-Martin/USPS SPBS Feed System Unloader, are bulky, with several degrees of freedom necessary for the unloading process and, consequently, several unloading stages and multiple actuators. In the unloading process, these devices generally take advantage of the constant feature that all BMCs unload through an open top thereof. Additionally these devices require the loading of the BMC into the device, not moving the device to the container. It is also difficult to use these unloaders in a confined indoor space, and ceiling heights in excess of 9 feet are often required.
xe2x80x9cIt would be desirable to have a BMC unloader which suitably upends and unloads a BMC with minimal actuation, causing rotational movement about the center of mass simultaneously with horizontal translation of the center of mass.xe2x80x9d
It would also be desirable for the movement associated with the unloading process to be capable of occurring in a confined indoor space, for example, with a maximum ceiling height requirement of no more than approximately 9 feet during any phase of operation.
It would also be desirable for a BMC unloading device and method to accomplish the unloading task in less time, in a smaller operational space, at less cost, and with greater reliability than existing devices and methods designed for the same task.
Crossed 4-bar linkages are a well known mechanism for producing substantially straight line motion. The motion of a point on a device attached to the linkage approximates a straight line, replacing the need for a slider joint. However, with a suitable choice of crossed 4-bar linkage design, and in particular, with a suitable specification of various dimensions and proportions for the bars and pivot point separations of a crossed 4-bar linkage, the entire attachment can be moved in a way that is highly suitable for unloading, and that is not disclosed or suggested by the prior art.
In particular, a Bulk Mail Container (BMC) unloader in a preferred embodiment of the invention uses a simple crossed four bar-linkage of certain specified dimensions and proportions to move a predetermined point on a BMC unloader in a substantially straight line while the overall BMC unloader rotates about that predetermined point so as to upend the BMC container. This takes advantage of the crossed four-bar""s substantially straight-line motion over a limited range of its motion, as well as the rotational motion of the particular unloader link disclosed herein.
In use, a BMC container is simply rolled into the BMC unloader, and the entire combination of the BMC container and BMC unloader is then actuated to produce substantially straight line motion along a suitably selected xe2x80x9ccenterxe2x80x9d point of the BMC unloader, while the overall container/unloader combination rotates about this center point so as to upend the BMC for unloading.